1. Field of the Invention
The present invention relates to a voice mail system for a switching network, and more particularly to a control system for a voice mail system.
2. Description of the Related Art
FIG. 1 shows a voice mail system to which a voice data transfer system disclosed in Japanese Patent Laid-open Application No. 164729/94 is applied.
Referring to FIG. 1, voice mail system 20 is provided together with switching system 10. Voice mail system 20 includes buffer memory (hereinafter referred to as RAM) 20a, disk unit (hereinafter referred to as DK) 20b, and CPU 20c, and is connected to switching system 10 via downward highway 30a and upward highway 30b.
Voice data sent from subscriber 40 are transferred to voice mail system 20 via switching system 10 and downward highway 30a. The voice data are stored once into RAM 20a under the control of CPU 20c in voice mail system 20. The stored voice data are written in a fixed amount into RAM 20a and then written from RAM 20a into DK 20b.
The first problem of the prior art described above resides in that the expandability of the system is low. The reason for this is that, of the two possible ways of coping with an increase in the number of subscribers and the volume of voice data, the parts increase method, whereby the number of RAMs installed is increased or the capacity of the disk unit is increased, is limited by the processing capacity of the CPU and the apparatus increase method, whereby an additional voice mail system is installed requires distribution processing to be performed by a switching system side which requires modifying the software of the switching system.
The second problem of the prior art described above resides in that the reliability of the system is low. The reason for this is that, since the voice mail system is provided together with the switching system, if the voice mail system fails partially, then all services are stopped and subscribers accommodated in the switching system connected to the voice mail system cannot enjoy voice mail services any more. In other words, since a buffer memory and a disk unit are coupled closely to each other in one apparatus, even if the disk apparatus operates normally, if an interface between the switching system and the voice mail system or the buffer memory suffers from a trouble, then it is difficult to continue services.
The third problem of the prior art described above resides in that the processing capacity of the system at the busiest time is low. The reason for this is that, since the voice mail system is provided together with the switching system, if subscribers accommodated in the same switching system request for services at the same time, then requests for processing are concentrated in the particular voice mail system, and consequently, it is difficult to process traffic at the busiest time in a decentralized manner and the processing capacity is degraded extremely.
The fourth problem of the prior art described above resides in that the maintainability of the system is low and it is difficult for the system to cope with new services. The reason for this is that, since the prior art has such a simple structure that the voice mail system is provided together with the switching system, when it is necessary to add new services in accordance with requests of individual users, the hardware and the software of the voice mail system must be modified all along the line. In other words, in modifying the hardware, an operation of stopping the voice mail system totally and exchanging the voice mail system is required, and in modifying the software, since a service executable program is executed by each individual voice mail system, it is required to stop the programs of the voice mail systems and rewrite the executable programs totally.